Question-and-Answer Resource for the Building Energy Modeling Community
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@Rohit Jogineedi: I can explain what's happening here. There's currently a bug in how the battery model was implemented in EnergyPlus related to how to account for the round trip efficiency of the battery (see https://github.com/NREL/EnergyPlus/issues/9176). To work around this and still track losses, we added an EMS program that takes the losses into account as additional energy consumption, but it only applies during charging, not discharging. We have a note about this in the documentation (https://openstudio-hpxml.readthedocs.io/en/latest/workflow_inputs.html#hpxml-batteries): "The round trip efficiency affects charging; the reported charging rate will be larger than the schedule value by an amount equal to the losses due to the round trip efficiency." If you apply the round trip efficiency to charging I'm pretty sure this will net out to 0.
Let me know if you have any additional questions about the battery model, I did the bulk of the implementation on this one. When the EnergyPlus issue is fixed we'll switch to a more direct model for accounting for battery losses rather than this EMS workaround.
